Electrodialysis apparatus



Aug. 3, 1965 P. KOLLSMAN 3,198,725

ELECTRbD IALYS I S APPARATUS Original Filed Dec. 9, 1957 3 Sheets-Sheet1 Fig. 1

2a E c D 29 20 455 0 l7 3! I I6 INVENTOR. Paul Kollsman 40 -H-M 4;, M

Fig. 2

ATTORNEY IN V EN TOR.

ATTORNEY Aug. 3, 1965 P. KOLLSMAN ELECTRODIALYSIS APPARATUS OriginalFiled Dec. 9, 1957 3 S tse 2 Paul Kollsman W QQ Fig. 4

w W w 3, 1965 P. KOLLSMAN 3,198,725

ELECTRODIALYSIS APPARATUS Original Filed Dec. 9, 1957 3 Sheets-Sheet 3INVENTOR. Paul Kollsman branes.

United States Patent 3,198,725 ELECTRGDEALYSKS APPARATUS Paui Kollsman,1% E. Stith St, New York 22, N.Y. Continuation of application Ser. No.701,457, Dec. 9, 1957. This appiication May 18, 1961, Ser. No. 111,071

The portion of the term of the patent subsequent to July 15, 1974, hasbeen dedicated to the Public 6 Claims. (Ci. 2ll4301) This application isa continuation of my copending application Serial No. 701,457, filedDecember 9, 1957, abandoned after the filing of this application.Application Serial No. 701,457 is a continuation-in-part of my earlierapplication Serial No. 350,377, filed April 22, 1953.

This invention relates to apparatus for modifying the chemicalcomposition of fluids by a controlled transfer of ions from, or into,selected fluid volumes under the influence of an electric current.

The transfer of ions takes place through semi-permeable walls separatinga volume of fluid from which ions are to be withdrawn from the volume offluid into which ions are to be transferred. The walls, also calledmembranes or diaphragms, are semi-permeable in the sense that theypermit certain ions to pass therethrough without permitting anequivalent amount of fluid or solvent to pass.

In an electro-dialyzer at least certain of the walls, membranes ordiaphragms are permselective in the sense that they are permeable toions of one polarity while being passage-resistant to ions of theopposite polarity.

Numerous materials are known, and are commercially available, which canbe shaped into thin walls and arranged in such a way that layers offluid and membranes alternate, the arrangement being that the electriccurrent traverses a plurality of membranes and fluid layers between theelectrodes.

In Helvitica Chimica Acta, vol. 23 (1940), pages 795 to '800, Meyer andStraus disclose a method of preparing anion permeable and cationpermeable membranes from Naturin, a treated collagen sheet material, andfrom treated cellophane, respectively. The manufacture of Naturin isdisclosed in United States Patent 2,114,220 to Freudenberg and Becker.

in 1950 Wyllie and Patnode described in considerable detail thepreparation and properties of improved membranes. In the Journal ofPhysical and Colloid Chemistry, vol. 54 (1950), pages 204 to 226, amethod is disclosed which involves the embedding of suitably ground ionexchange resins into a plastic matric by compression at an elevatedtemperature. These membranes which were originally developed for thedetermination of dialysis potentials are suited for ion transfer byelectrodialysis.

Anion resins and cation resins suitable for the preparation of membranesare available under a variety of trade names. The synthesis of suchmaterials is described by Kunin and Myers in Ion Exchange Resins, Wylieand Sons, 1950, beginning with page 54, and by Nachod in Ion Exchange,Academic Press, 1949, beginning with page 48. Both textbooks listcommercially available ion exchange resins by their respective tradenames, giving the names of their manufacturers and principalcomposition.

Electro-dialyzers of conventional construction generally comprise astack of spaced, substantially parallel mem- An electrode is at each endof the stack so that the electric current traverses the severalmembranes and the fluid layers between the membranes.

The efficiency and economy of operation of electrodialyzers ofconventional construction is impaired by the formation of polarizationlayers on the membrane surfaces. It is desirable to reduce or removethese polarization layers by an increase in the flow velocity of thefluid.

ice

This remedy, however, is generally not available because the flow pathin conventional electro-dialyzers is so short that a rapid flow of fluidis not exposed to the action of the electric current sufliciently longbetween the points of inflow and outflow to effect the desired transferof ions.

These and various other aims, objects and advantages of the inventionwill appear more fully from the detailed description which follows,accompanied by drawings showing, for the purpose of illustration,preferred forms of the invention.

The'invention also consists in certain new and original features ofconstruction and combination of parts, as here inafter set forth andclaimed.

Although the characteristic features of this invention, which arebelieved to be novel, will be particularly pointed out in the claimsappended hereto, the invention itself, its objects and advantages andthe manner in which it may be carried out, will be better understood byreferring to the following description taken'in connection with theaccompanying drawings, forming a part of it in which:

FIG. 1 is a horizontal cross-section through an apparatus embodying theinvention, the section being taken in plane 1-111 of FIG. 6;

FIG. 2 is a diagrammatic representation of the flow paths of theapparatus of FIG. 1;

FIG. 3 is a vertical cross-section through the apparatus of FIG. 1, thesection being taken on line33;

FIG. 4 is a vertical section through the apparatus of FIG. 1, thesection being taken on line 4-4;

FIG. 5 is a perspective view of a preferred form of seal for theapparatus of FIG. 3;

FIG. 6 is a perspective View of the complete apparatus;

FIG. 7 is a perspective view of a portion of a membrane employed in theapparatus of FIG. 5; and

FIGS. 8 and 9 show modified forms of membrane for the apparatus. a

In the following description and in the claims, various details will beidentified by specific names for convenience. The names, however, areintended to be as generic in their application as the art will permit.Like reference characters refer to like parts in the several figures ofthe drawings.

In the drawings accompanying and forming part of this specification,certain specific disclosure of the invention is made for the purpose ofexplanation of broader aspects of the invention, but it is understoodthat the details may be modified in various respects without departurefrom the principles of the invention, and that the invention may beincorporated in other structures than the ones shown.

The electro-dialyzer shown in the drawings comprises two end plates 11and 12, between which the membrane assembly 13 is mounted.

The membrane assembly essentially consists of two substantiallyrectangular membrane strips 14 and 15 of a Width substantially equal tothe spacing of the plates 11 and 12 and of a length which is optionaland depends entirely on the length of the flow path to be constructed.

One of the membranes is permeable to ions of one polarity and passageresistant to ions of the oppostie polarity, and the other membrane ispermeable to ions of the opposite polarity and is suitably, although notnecessarily, also passage resistant to ionsof the one polarity.

As is apparent from the drawings, particularly FIG. 1, the first and thesecond membrane strips are spirally coiled upon each other in such a wayas to leave fluid spaces 16 and 17 therebetween.

A first fluid space or passage 16 is formed between the membrane strip14 and the membrane strip 15, and a second fluid space 17 is formedbetween the membrane strip 15 and the succeeding turn of the membranestrip 14.

In order to form these fluid spaces or passages, spacers are employedwhich separate the body of one membrane a.) from the body of the nextmembrane. Such spacers may be separate elements, such as strips ofmembrane material, cellophane and the like, but are preferablyprotrusions integral with, and extending from, the body of themembranes.

As .shown in FIG. 6, such protrusions may have the form of ribs 18,integrally formed as part of the membrane strip. 'FIG. 8 illustrates analternate form of spacer in the form of substantially cylindrical studs19.

In the forms of the apparatus shown in FIGS. 1 to 8 each membrane stripis provided with integral spacers, but it is, of course, possible toemploy a double-faced membrane as shown in FIG. 9 in connection with aflat sheet membrane.

Marginal sealing ribs 21 and 22 are provided for sealing the edges ofthe coiled membrane strips. These marginal sealing ribs are preferablymade integral with the strip, like the spacer ribs, as shown in FIG. 6.Addi tional marginal seals of a suitable elastic sealing material may beemployed as shown at 23 in FIG. 5.

Terminal blocks 24 and 2.5 are arranged at the ends of the membranestrips, and the membrane strips are sealed in regard to these blocks asshown at 26 and 27. Ducts 28 and 29 lead into the block 24- and ducts 30and 31 lead into the block 25.

Fluid may be conducted through the apparatus in any desired direction.For example, the flows through the fluid passages 16 and 17 may be inthe same direction or in opposite directions. In the illustrated form ofapparatus flow in opposite directions is indicated.

Thus, fluid enters through duct 28 (see also FIG. 2) and flows throughthe passage 17 spirally towards the center, to leave the apparatusthrough the duct 31 at the end of the centermost turn of the fluidpassage 17.

A further flow of fluid enters at 30 .at the centermost turn of thefluid passage 16 and leaves the passage at the peripheral end throughthe duct 29.

The ducts 28, 29, 38 and 31 extend across the entire width of themembrane strips and constitute manifolds, in a sense, for the variousbranch passages formed by the spacer ribs 18. In the event spacer studsare employed, as shown in FIG. 8, there are of course no branch flows,but the fluid flows in the form of a ribbon, interrupted only by thestuds which impart a certain amount of turbulence to the flow.

A peripheral electrode 32 has a lead 33 and is sealed with regard to theterminal block 24 at 34. A similar electrode 35 constitutes the centerof the assembly and is sealed with respect to the terminal block 25 at36. A lead 37 extends from the center electrode to a suitable source ofelectrical potential.

The peripheral electrode 32 and the central electrode 35 are spaced fromthe respective outermost and innermost turns of the membrane assembly byspacers 3S and 39, respectively. These spacers are preferably ofcorrugated material as shown particularly in FIG. 3. The elec trodespacers form electrode chambers 40 and 41 through which fluid may flowbetween the electrode and the proximate turn of the membrane strip.

As shown best in FIG. 6, an inflow duct 42 is provided for theperipheral electrode chamber. This inflow duct extends through the endplate 11. A corresponding out flow duct 43 extends from the peripheralelectrode chamber through the other end plate 12.

Similarly, a central inflow duct 44 for the electrode chamber 41 extendsthrough the end plate 11 and a central outflow duct 45 leaves theelectrode chamber 41 through the end plate 12.

The apparatus may be operated as follows:

It may be assumed that an ionic solution is to be deionized by transferof ions into another fluid whose ionic concentration is correspondinglyincreased thereby. As a specific example, it may be assumed that seawater is to be desalted.

The solution to be deionized is preferably fed into the the fluidpassage 16. The fluid flows along a spiral path outwardly and finallyleaves the apparatus through the duct 29. The fluid into which the ionsare to be transferred is fed into the apparatus preferably through theduct 28, through which it enters into the fluid passage 17 to flow alonga spiral path inwardly. As it does so, the ions of the fluid in passage16 move through the bordering membrane walls into the adjoining passages17 in such a way that the cations travel towards the cathode, which maybe the electrode 32, the anions travelling towards the shore, which maybe the electrode 35.

It is apparent from the dimensions of the apparatus that the currentdensity is necessarily greater near the center of the apparatus than itis near the periphery. The fluid to be deionized is subjected to apowerful deionizing action immediately after entry into the apparatus.The fluid loses its ions rapidly, which are being transferred into thefluid flow within the fluid passage 17. The fluid entering this passageis preferably of a hi h degree of purity, so that fluid leakage throughthe membrane, which exists to some extent in all present commercialmembranes, will not contaminate the fluid to be deionized. As the fluidWithin the passage 17 nears the center, it is being ionenriched withprogressive rapidity. It will be noted that the current density near thecenter is not only high because of the physical construction of theapparatus, but also because of the relatively high ionic concentrationof the fluid in the passages adjacent the center.

Polarization layers are effectively removed, or at least reduced to anappreciable extent, by the rapid flow rate of the fluid which ispreferably of the order of one to twenty inches per second. Since theflow paths are extremely long, for example of the order of 50 to feetfor an apparatus having an external diameter of approximately 12 to 20inches and employing membranes of approximately 1 to 2 mm. thickness andl to 2 mm. spacing, the fluid may flow at a high velocity while yetremaining under the action of the electric current for a suflicient timebefore it leaves the apparatus. This velocity may be the greater thegreater the number of turns through which the fluid flows. -It is alsoevident that an addition of several turns lengthens the flow pathappreciably, thus permitting a substantial increase in flow velocity,without materially increasing the diameter of the apparatus.

Large or small volumes of fluids are accommodated by an appropriateselection of the width of the membrane strips, that is, the spacingbetween the end plates 11 and 12.

An apparatus was constructed from two strips of Meyer and Strausmembrane material of approximately 600 mm. length .and 50 mm. width. Theinner electrode had a diameter of 50 mm. around which the membranestrips were wound. The membrane strips were spaced by three strips ofsoft rubber sheet material of 2 mm. thickness and 5 mm. width which werewound up together with the membranes to form sealed spiral shapedchambers. The chambers were sealed along the margin by two of the rubberstrips and the third rubber strip was used as a spacer along the centerof the membrane The electrode chambers were equipped with spacers of athermoplastic screen material of 2 mm. thickness and 6 mm. mesh size.The membrane strip nearest the center electrode consisted of anionexchange material, the other membrane consisted of cation exchangematerial. The electrodes were shaped of sheet platinum and formedsubstantially complete rings. Each spiral chamber had an inner and anouter duct connection. Each electrode chamber also had an inlet and anoutlet duct at each end. The central electrode was an anode and theouter electrode was a cathode.

Solution of 0.1% NaCl in water, acidified with hydrochloric acid to a pHof 4.5 was supplied into the concentration and dilution chambers and acurrent of 100 um. was maintained. Saline solution was supplied into thepheripheral duct of the spiral chamber and concentrate was withdrawnadjacent the inner electrode. A second apparatus through the duct :30through which it enters flow of saline solution was maintained throughthe deionization chamber, the supply point being adjacent the centralelectrode and the withdrawal point adjacent the peripheral electrode.The flow rate to each outflow duct was 5 cc. per minute. The flow ratethrough each electrode chamber was 20 cc. per minute.

After 60 minutes of operation the liquid withdrawn at the peripheraloutflow duct had a concentration of 0.023 NaCl in water, correspondingto a reduction of the sal content by 77% during passage of the liquidthrough the spiral deionization chamber.

A second apparatus was constructed with membranes prepared according tothe aforementioned disclosure of Wyllie and Patnode. The membranes wereof a thickness of about 0.5 mm. Air dried Amberlite IRA400 of 120 meshsize was used for the anion membranes and air dried Amberlite IR-120 of120 mesh size was used for the cation membranes. The Amberliteconstituted 70% of the total membrane material, the balance beingpolystyrene binder material. The membrane strips were approximately 600mm. in length and 50 mm. in width. Three strips of soft rubber of 2 mm.thickness and 5 mm .width served as spacers and the construction of theapparatus corresponded to the apparatus previously described equippedwith Meyer and Straus membranes.

Solution of 0.1% NaCl in water was fed into the apparatus without anyaddition of hydrochloric acid, and a cur-rent of 100 ma. was maintained.The operational data corresponded to those of the previous example.

After 60 minutes of operation the liquid withdrawn at the peripheraloutflow had a concentration of 0.017% NaCl in water, corresponding to areduction of the salt content by 83%.

In an apparatus embodying the invention, operated to pass the diluteflow through the apparatus in an outw direction, the current density islowest across the portion of the dilute flow where the electricalresistance is the highest. The high flow velocity results in aneffective reduction of polarization, particularly in the dilute portionwhere such reduction is most important.

What is claimed is: V

1. In an electrodialysis apparatus comprising spaced electrodes, thecombination, between the electrodes, of two spaced membranes of ionexchange material defining a liquid passage between them including apassage entrance and a passage exit for liquid passing through thepassage; and a flow obstacle structure, said structure comprising aplurality of individual flow obstacle elements of ion exchange materialextending from one membrane through said passage to the other membrane,said elements being laterally as well as longitudinally spaced from oneanother within said passage to obstruct liquid flowing through saidpassage and produce turbulence by the repeated dividing and recombiningof the liquid flow at each individual element.

2. In an electrodialysis apparatus comprising spaced electrodes, thecombination, between the electrodes, of two spaced membranes of ionexchange material defining a liquid passage between them including apassage entrance and a passage exit for liquid passing through thepassage; and a flow obstacle structure, said structure comprising aplurality of individual flow obstacle elements of ion exchange materialextending from one membrane through said passage to the other membrane,said elements being laterally as well as longitudinally spaced from oneanother within said passage and interconnected to maintain the spacingbetween the said elements, said elements obstructing the liquid flowingthrough said passage and producing turbulence by the repeated dividingand recombining of the liquid flow at each said element.

3. In an electrodialysis apparatus comprising spaced electrodes, thecombination, between the electrodes, of two spaced membranes of ionexchange material defining a liquid passage between them including apassage entrance and a passage exit for liquid passing through thepassage; and a flow obstacle structure of ion exchange material, saidstructure comprising a plurality of individual flow obstacle elementsintegral with at least one membrane and extending into the liquidpassage into substantial contact with the other membrane, said elementsbeing laterally as well as longitudinally spaced from one another withinsaid passage to obstruct liquid flowing through said passage and produceturbulence by the repeated dividing and recombining of the liquid flowat each individual element.

4. In an electrodialysis apparatus comprising spaced electrodes, thecombination, between the electrodes, of two spaced membranes of ionexchange material defining a liquid passage between them including apassage entrance and a passage exit for liquid passing through thepassage; and a flow obstacle structure of ion exchange material, saidstructure comprising a plurality of individual flow obstacle elements ofion exchange material, said elements being integral with one membraneand extending through the liquid passage into contact with the othermembrane, said elements being laterally as Well as longitudinally spacedfrom one another within said passage to obstruct liquid flowing throughsaid passage and produce turbulence by the repeated dividing andrecombining of the liquid flow at each individual element.

5. A liquid turbulence promoting membrane spacing structure forelectrodialysis cells, said structure comprising an assembly ofindividual elements of ion exchange material, said elements beinglaterally as well as longitudinally spaced from one another in the flowpath to obstruct the liquid flow and produce turbulence by the repeateddividing and recombining or" the flow at each individual element; andmeans for interconnecting said elements to maintain their spacing fromone another, said elements having opposite end surfaces lying in twospaced substantially parallel planes.

6. A structure for the promotion of turbulence in a liquid flow channelof an electrodialysis cell, said structure comprising a plurality ofindividual elements of ion exchange material, said elements beinglaterally as well as longitudinally spaced from one another in the flowchannel to obstruct the liquid flow and produce turbulence by therepeated dividing and recombining of the flow at each element; and asheet of ion exchange material interconnecting said elements to fix thedistance between said elements, said sheet forming one plane of thestructure, the said elements having surfaces lying in a second planespaced from, and substantially parallel to, said first plane.

References Cited by the Examiner UNITED STATES PATENTS 2,741,595 4/56Juda 204--260 2,799,644 7/57 Kollsman 204-301 2,802,344 8/57 Witherell204-301 2,815,320 12/57 Kollsman 204301 2,948,668 8/60 De Whalley et al.204-301 3,014,855 12/61 Kressman 204301 FOREIGN PATENTS 555,471 3/23France. 652,442 4/51 Great Britain.

WINSTON A. DOUGLAS, Primary Examiner.

JOHN R. SPECK, JOHN H. MACK, Examiners.

1. IN AN ELECTRODIALYSIS APPARATUS COMPRISING SPACED ELECTRODES, THECOMBINATION, BETWEEN THE ELECTRODES, OF TWO SPACED MEMBRANES OF IONEXCHANGE MATERIAL DEFINING A LIQUID PASSAGE BETWEEN THEM INCLUDING APASSAGE ENTRANCE AND A PASSAGE EXIT FOR LIQUID PASSING THROUGH THEPASSAGE; AND A FLOW OBSTACLE STRUCTURE, SAID STRUCTURE COMPRISING APLURALITY OF INDIVIDUAL FLOW OBSTACLE ELEMENTS OF ION EXCHANGE MATERIALEXTENDING FROM ONE MEMBRANE THROUGH SAID PASSAGE TO THE OTHER MEMBRANE,SAID ELEMENTS BEING LATERALLY AS WELL AS LONGITUDINALLY SPACED FROM ONEANOTHER WITHIN SAID PASSAGE TO OBSTRUCT LIQUID FLOWING THROUGH SAIDPASSAGE AND PRODUCE TURBULENCE BY THE REPEATED DIVIDING AND RECOMBININGOF THE LIQUID FLOW AT EACH INDIVIDUAL ELEMENT.
 5. A LIQUID TURBULENCEPROMOTING MEMBRANE SPACING STRUCTURE FOR ELECTRODIALYSIS CELLS, SAIDSTRUCTURE COMPRISING AN ASSEMBLY OF INDIVIDUAL ELEMENTS OF ION EXCHANGEMATERIAL, SAID ELEMENTS BEING LATERALLY AS WELL AS LONGITUDINALLY SAPCEDFROM ONE ANOTHER IN THE FLOW PATH TO OBSTRUCT THE LIQUID FLOW ANDPRODUCE TURBULENCE BY THE REPEATED DIVIDING AND RECOMBINING OF THE FLOWAT EACH INDIVIDUAL ELEMENT; AND MEANS FOR INTERCONNECTING SAID ELEMENTSTO MAINTAIN THEIR SPACING FROM ONE ANOTHER, SAID ELEMENTS HAVINGOPPOSITE END SURFACES LYING IN TWO SPACED SUBSTANTIALLY PARALLEL PLANES.